Producing electrolytic manganese



United States Patent Ofiice 2,814,591 Patented Nov. 26, 1957 PRODUCINGELECTROLYTIC MANGANESE Reginald S. Dean, Hyattsville, Md.

No Drawing. Application November 22, 1954, Serial No. 470,527

3 Claims. (Cl. 204-105) This invention relates to processes forproducing electrolytic manganese, and has for its object the productionof electrolytic manganese in a single compartment cell utilizing anelectrolyte of manganese and ammonium chlorides and a graphite anode.

The chloride electrolyte has been found to have many advantages butoxidation at the anode has presented many problems. In my copendingapplication Serial No. 395,807, filed December 2, 1953, I have disclosedmeans of overcoming much of this difliculty by suspending an oxidicmanganous compound such as manganese carbonate in the electrolytewhereby to control the pH and to replenish the manganese content of theelectrolyte.

The presence in the electrolyte of a reduced compound of sulphur,preferably the sulphite ion, is necessary to obtain good efficiency.With high current density and the chloride electrolyte consumption ofsulphite is large.

I have found that the sulphite oxidation at the anode may be greatlyreduced by adding certain reducing agents to the electrolyte in additionto sulphite. The agents of my invention are hydroxylamine and hydrazinesalts and related compounds.

In my U. 8. Patent No. 2,316,937, issued April 20, 1943, I disclosedhydroxylamine salts and similar compounds as antioxidants added tomanganese ammonium sulphate solutions in the cathode compartment of adiaphragm cell for the production of electrolytic manganese. The presentinvention is concerned with anodicnot cathodic-behavior, and isspecifically directed to an electrolysis involving chloride electrolytescontaining sulphite. It is also specifically directed to singlecompartment cells having a graphite anode.

The purpose of the hydroxylamine and hydrazine salts of my invention isto depolarize the anode in such a way that the oxidation of the sulphiteion present is greatly reduced without substantial oxidation of thehydrazine, hydroxylamine and the like.

The practice of my invention permits the use of manganese carbonate, inaccordance with my copending application previously referred to, whichcontains considerable iron as ferrous carbonate. The iron dissolved atthe anode in the presence of sulphite and the other reducing agent of myinvention is oxidized to an insoluble magnetic iron compound, which ispresent as separate particles in the suspension. The iron may be removedfrom the suspension by a high-intensity magnetic separator such as theFranz Ferrofilter.

The reducing compounds of my invention include in addition to salts ofhydroxylamine and hydrazine the substituted compounds of this class suchas phenyl hydrazine, hydrazones, and oximes.

Having now described my invention, I will illustrate it by severalexamples:

Example I I take an electrolyte composed of:

12-16 grams per liter Mn as chloride 125 grams per liter NH CI 5-10grams per liter suspended manganese carbonate 0.1 gram per liter S0 0.5gram per liter hydrazine hydrochloride I adjust the pH of this solutionto 6.2. I then pass this electrolyte between a titanium cathode and agraphite anode, in a single-compartment electrolytic cell, at such arate that the pH of the electrolyte leaving the cell is 5.5 The currentdensity on the electrodes is amperes per square foot. Manganese of highpurity is deposited on the cathode at a current efliciency of 69.5%.Analysis of the exit electrolyte shows a consumption of S0, of 0.1 gramper gram of manganese deposited. The loss of hydrazine is less than .001gram per gram of manganese deposited.

The pH and manganese content of the exit electrolyte are brought to theoriginal values by stirring with manganous carbonate.

Example II I proceed as in Example I, except that I substitute 1.0 g./liter hydroxylamine hydrochloride for the hydrazine salt. The resultsobtained are substantially identical with those in Example I.

Example III In this example I proceed as in Example I using a manganesecarbonate containing 0.23% Fe as ferrous iron I pass the electrolyte andsuspended material through the cell, in the manner described, until theweight of suspended carbonate is reduced one-half. During this time thedeposition of manganese has proceeded at good efliciency. I then passthe electrolyte and its suspended carbonate through a Franz Ferrofilterand remove a magnetic fraction analyzing 5.2% iron. The electrolyteleaving the cell during this experiment was iron-free.

I claim:

1. In a process for the electrodeposition of manganese in a singlecompartment cell having a graphite anode, a cathode of chemically inertmetal and an electrolyte of manganese and ammonium chlorides containingsulphite ion and suspended manganese carbonate, the improvement whichconsists in minimizing oxidation of sulphite ion at the anode by theaddition to the electrolyte of a reducing agent selected from the groupconsisting of salts of hydrazine, and salts of hydroxylamine, at aconcentration within the range 0.1-1.0 gram per liter.

2. In a process for the electrodeposition of manganese in a singlecompartment electrolytic cell having a graphite anode and a cathode ofchemically inert metal, in which process there is continuouslycirculated through the cell an aqueous electrolyte of manganese andammonium chlorides containing sulphite ion at a concentration within therange ODS-0.3 gram per liter and suspended manganese carbonate, theimprovement which consists in minimizing oxidation of sulphite ion atthe anode by including in the electrolyte a reducing agent selected fromthe group consisting of salts of hydroxylamine and salts of hydrazine,at a concentration within the range 0.1-1.0 gram per liter, adjustingthe pH of the electrolyte before each passage through the cell to about6, passing the electrolyte through the cell at such a rate that the pHof of the electrolyte leaving the cell is about 5.5, and be 4 fore eachreuse adding to the electrolyte and stirring References Cited in thefile of this patent therein additional manganese carbonate in an amountto UNITED STATES PATENTS replenish the original manganese content of theelectrolyte.

3. The process of claim 2, further characterized by 2,119,560 Shawn June1938 the manganese carbonate containing ferrous iron, the exit 52317-153 Dean P 1943 pH being at least 5.5, and the additional step ofperiodi- 2,546,547 Koster 1951 cally magnetically separating the ironfrom the suspended REFERENCES mammal m the electrolyte Jacobs et 211.:U. S. Bureau of Mines Report of Investi- 10 gation 4817, September 1951,pages 6 to 13.

1. IN A PROCESS FOR THE ELECTRODEPOSITION OF MANGANESE IN A SINGLECOMPARTMENT CELL HAVING A GRAPHITE ANODE, A CATHODE OF CHEMICALLY INERTMETAL AND AN ELECTROLYTE OF MANGANESE AND AMMONIUM CHLORIDE CONTAININGSUIPHITE ION AND SUSPENDED MANGANESE CARBONATE, THE IMPROVEMENT WHICHCONSIST IN MINIMIZING OXIDATION OF SULPHITE ION AT THE ANODE BY THEADDITION TO THE ELECTROLYTE OF A REDUCING AGENT SELECTED FROM THE GROUPCONSISTING OF SALT OF HYDRAZINE, AND SALTS OF HYDROXYLAMINE, AT ACONCENTRATION WITH THE RANGE 0.1-1.0 GRAM PER LITER.